In the episode where Jack is reminiscing of the past Young Jack sees a man fighting 4 figures on a bridge. The man pushes his son in a wooden cart. This is a reference to a Japanese movie franchise called Lone Wolf and Cub from the 70's. The protagonist, Ogami , Itto is a former executioner on behalf the Emperor, now forced to roam the lands with his son, Daigoro, as a sellsword - ever seeking justice for the crimes committed against his family.